Inadequate and inaccurate depth measurement following orthopedic drilling procedures may result in incorrect screw lengths, which can lead to surgical complications. Furthermore, determining the correct screw length for a bore can be a time consuming procedure which is undesirable when tissue is exposed and potentially subjected to infection.
As shown in FIGS. 1A and 1B, the bony structure of the human anatomy consists mainly of cortical bone 10 having a hard outer cortex 12 and a soft inner medullary layer 14. Following traumatic injury, plate and screw placement is critical for adequate repair of a fractured bone. Improper drilling lengths could lead to device instability, damage to anatomic structures, or device failure.
As shown in FIG. 1A, when using a rotating drill bit 16 to form a bicortical bore 18 through the cortical bone 10, the rotating drill bit 16 passes through a first portion 12a of the hard outer cortex 12, a soft non-resistant medullary layer 14, and a second portion 12b of the hard outer cortex 12.
As shown in FIG. 1B, when using a rotating drill bit 16 to form a unicortical bore 20 through the cortical bone 10, the rotating drill bit 16 passes through an entry point 22a of the hard outer cortex 12 and an exit point 22b of the hard outer cortex 12 without penetrating the soft non-resistant medullary layer 14.
Previously proposed techniques for drilling and screw placement have been two-step processes, at best. For example, during an operation, a bore is first drilled by a surgeon until the surgeon “feels” the drill bit pass completely through the bony structure. That is, the surgeon must rely on his or her senses alone to determine when the drill bit has passed completely through the bony structure. Once the surgeon believes that he or she has passed completely through the structure, the drill bit is removed from the bore and a depth gage (not shown) is then inserted into the bore. The depth gage is grasped against the proximal end and a depth is recorded. A possible resulting complication of this procedure is that the surgeon may not precisely “feel” the drill bit pass through the second cortical layer, thereby possibly damaging tissue on the opposite side of the bone. Another complication may occur if the depth gage is not properly inserted into the hole. If the gage is grasped prior to passing the distal end of the bore, a size will be determined that is smaller than the true depth.
The process of drilling and depth measurement often requires more than one attempt. Conservative drilling may result in incomplete drilling requiring multiple passes. Furthermore, multiple depth measurements may be required to confirm accurate placement of the gage. This process consumes a substantial amount of surgical time resulting in a large cost per patient. By combining the drilling and depth measurement process into one accurate procedure, cost is reduced along with a decrease in patient morbidity.